An iterable ni kitu chochote unachoweza kuzunguka juu yake (orodha, kamba, dict); an iterator ni kitu kinachofanya iteration halisi, kutengeneza thamani moja kwa wakati mmoja na kusulili nafasi yake. Tofauti hii iko chini ya jinsi for loops zinavyofanya kazi katika Python.
Iterable → has __iter__() → returns an iterator
Iterator → has __next__() → returns the next value (and __iter__ returning itself)
# this for loop...
for x in [1, 2, 3]:
print(x)
# ...is roughly equivalent to:
it = iter([1, 2, 3]) # __iter__ → get an iterator from the iterable
while True:
try:
x = next(it) # __next__ → get the next value
print(x)
except StopIteration: # raised when exhausted → loop ends
break
A for loop inaita iter() kupata iterator, kisha inaitia next() mara kwa mara hadi StopIteration isigeze mwisho. Mfumo huu ndio unayofanya iterable ionekane.
nums = [1, 2, 3] # an ITERABLE (a list)
it = iter(nums) # an ITERATOR over it
next(it) # 1
next(it) # 2
next(it) # 3
next(it) # StopIteration
# the list is REUSABLE (get a fresh iterator each loop);
# an iterator is CONSUMED ONCE — exhausted after one pass
list(it) # [] — already used up
Tofauti kuu: iterable (orodha) inaweza kuzunguka mara nyingi (kila for inapata iterator mpya); iterator ni matumizi moja — baada ya kuishia, iko tupu.
class Countdown:
def __init__(self, start): self.n = start
def __iter__(self): return self # the iterable returns itself as iterator
def __next__(self):
if self.n <= 0:
raise StopIteration # signal the end
self.n -= 1
return self.n + 1
for x in Countdown(3): # 3, 2, 1
print(x)
def gen(): yield 1; yield 2 # a generator function returns an iterator automatically
Generators ni njia rahisi ya kujenga iterators — yield inashughulikia __next__/StopIteration kwa ajili yako.
Tofauti ya iterable/iterator inaeleza jinsi for loops zinavyofanya kazi katika Python na jinsi iteration iko umoja katika collections zote (orodhamu, dicts, faili, generators) kupitia mfumo wa iterator.
Kuielewa kunajasiri tabia halisi — kwa nini iterator inaweza kuishia mara moja tu (kosa la kawaida: kuzunguka generator/zip mara mbili hakuna kitu kwa wakati wa pili), kwa nini generators ni iterators, na jinsi ya kufanya vitu vyako iterable.
Mfumo huu ndio msingi wa mfumo wa iteration wa Python ambao ni nyumbuzi, thabiti na iko muhimu sana wakati wa kufanya kazi na generators, tathmini ya upindi, na darasa la iterable la kawaida.